Entergy Louisiana announced plans Thursday to build a new 550-megawatt natural gas unit at its Ninemile Point plant in Westwego.

Susan Poag, The Times-PicayuneBill Mohl, president and CEO of Entergy Louisiana, announces plans Thursday to build a 550-megawatt natural gas unit at its existing Ninemile Point plant in Westwego.

The utility filed paperwork with the Louisiana Public Service Commission on Tuesday seeking permission to build the $721 million, combined-cycle gas-turbine unit. The project is expected to create upward of 600 temporary jobs at the peak of construction, and an additional 17 long-term positions, responsible for managing the unit, officials said Thursday.

If approved by state regulators, construction on the unit is slated for 2012, and it is expected to enter commercial operation by mid-2015. Entergy New Orleans, which provides electricity on the east bank of Orleans Parish, is expected to receive about 20 percent of the power generated at the facility, while Entergy Gulf States, which serves areas between Baton Rouge and Texas, will receive about 25 percent of the output, Bill Mohl, president and chief executive officer of Entergy New Orleans, said at a press conference at the plant Thursday.

Entergy officials, who plan to ask the Public Service Commission for permission to recover the full cost of the project from ratepayers over the course of several decades, say the unit will be among the cleanest gas-fired generating plants in the nation, and could produce fuel savings for customers ranging from $26 to $53 million per year.

The utility has contracted with the Baton Rouge-based Shaw Group to manage construction of the unit.

Unlike older, conventional gas-fired power plants, combined-cycle gas-turbine units are considered more efficient because they use turbines that operate by the combustion of compressed air and fuel, which powers a turbine generator that produces electricity. Steam from the combustion is then recovered and used to power a steam turbine generator, which generates additional energy without using more fuel.

Earlier this year, Entergy Louisiana announced that it had completed a $300 million acquisition of Acadia Energy Center Power Block 2, a 580-megawatt combined-cycle gas-turbine generation facility south of Eunice.